Method and Device for the Thermal Treatment of Waste Materials

ABSTRACT

The present invention relates to a method for the thermal treatment of waste materials of all types, in which the waste is subjected to a high temperature treatment with oxygen at temperatures of above 1000° C., the organic waste components being gasified. The thereby resulting synthesis gas is removed from the high temperature reactor uncooled and uncleaned and subsequently is oxidised. The thereby resulting thermal energy of the waste gas is further used thermally. The present invention likewise relates to a corresponding device for the thermal treatment of waste of all types.

The present invention relates to a method for the thermal treatment of waste materials of all types, in which the waste is subjected to a high temperature treatment with oxygen at temperatures of above 1000° C., the organic waste components being gasified. The thereby resulting synthesis gas is removed from the high temperature reactor uncooled and uncleaned and subsequently oxidised. The thereby resulting thermal energy of the waste gas is further used thermally. The present invention likewise relates to a corresponding device for the thermal treatment of waste of all types.

In the patent specifications DE 41 30 416 C1 and UA 41 263 C2, a method for the disposal and utilisation of waste of all types is described, in which unsorted, untreated, industrial, domestic and special waste containing pollutants of whatever type in solid and/or liquid form and also industrial material scrap are subjected to a temperature treatment.

These disposal methods known from the state of the art have however the disadvantage that a substantial part of the recovered energy is lost during shock-cooling (quenching) of the synthesis gas.

It is hence the object of the present invention to indicate an improved disposal method and also an improved disposal device of the above-mentioned type, with which as high a proportion of the energy as possible can be utilised.

This object is achieved with respect to the method by the features of patent claim 1 and, with respect to the device, by the features of patent claim 11. The respective dependent claims thereby represent advantageous developments.

According to the invention, a method for the thermal treatment of waste of all types is hence provided, in which the waste is subjected to a high temperature treatment with oxygen and/or air enriched with oxygen at a temperature of above 1000° C., the organic waste components being gasified, the inorganic waste components being melted, the uncooled, uncleaned synthesis gas being oxidised and the thereby obtained waste gas being used thermally.

The waste is firstly compacted whilst maintaining the mixture and composite structure thereof in order to minimise the void volume. The resulting compacted bales are pressed into an externally heated oblong channel, a gas-tight plug forming in front of the channel entrance, which adopts a seal function because of the gas impermeability thereof.

Whilst the gas pressure is building up, the compacted bales are retained in frictional contact with the hot channel walls only until the entrained liquids and readily volatile materials are evaporated and any restoring forces present of individual components are eliminated and until the entrained organic components have adopted at least partially a binding agent function. After a short dwell time of the disposal material in the heated channel, a compact shaped billet is produced, in which the fine components and dusts introduced with the waste material are bonded. The result hence is dust-free, form-stable and structure-stable crumbly conglomerates which, subsequently in a preferred embodiment, fall into the shaft of a high temperature gasifier or high temperature reactor and form a gas-permeable, dust-free bed.

The organic components are gasified by the addition of oxygen. Because of the hereby resulting gasifying temperature, the inorganic components, i.e. all glasses, metals and other minerals, are melted in the melting zone of the high temperature reactor at temperatures of up to 2000° C. below the bed. The withdrawn melt is however characterised, in the case of waste material supplied unsorted, still by an extensively non-homogeneous structure. Higher-melting components, for example carbon but also specific metals, are still present in their solid aggregate state and form inclusions so that useful recovery of these slag-like residual products is impossible.

The residual products present in molten form are therefore preferably subjected to an additional subsequent treatment in that they are subjected to a thermal homogenisation process. The melt is hereby cleansed in an oxidising atmosphere until a homogeneous high temperature melt is present so that even long-term ability to be eluted is precluded.

The high temperature reactor is characterised in that it is maintained at at least 1000° C. over the entirety of its volume.

The gaseous and solid waste materials remain subjected to a high temperature treatment until all the pollutants able to react thermally are safely destroyed and long-chain hydrocarbons are cracked. As a result, the formation of condensates, such as tars and oils, is reliably prevented.

According to the invention, it is now proposed to supply the thus produced uncooled and uncleaned synthesis gas which is heated above 1000° C. for energy use.

As a result of the present invention, the energy obtained by the gasification of waste with pure oxygen is used optimally. This method represents furthermore—compared with the state of the art—not only a substantial simplification but it also leads to a significant reduction in specific investment and operational costs. As a result of the energy savings which are achieved, the method according to the invention is clearly advantageous also from ecological aspects.

The gaseous phase comprises synthesis gas obtained by the gasification of the organic waste components and steam which can be attributed above all to the moisture contained in the waste. Since the gaseous phase leaves the high temperature reactor at a temperature of approx. 1000° C., thermal energy is bonded in this hot gaseous phase. In addition, the synthesis gas has available chemical energy with its combustible components.

If the gaseous phase is shock-cooled by injection of cold water to <100° C., as has been done previously in the state of the art, the entire thermal energy of the gaseous phase is lost. Only the chemical energy bonded in the synthesis gas can be used.

With the present invention, not only the chemical energy bonded in the synthesis gas but also the thermal energy of the entire gaseous phase will hence be used in that firstly the uncooled and uncleaned synthesis gas is oxidised, preferably combusted slightly overstoichiometrically. This oxidation step is thereby implemented preferably in at least one combustion chamber which is disposed separately, i.e. outwith the high temperature reactor. A hot waste gas is thereby obtained so that the gaseous phase comprises hot steam and hot waste gas from the combustion of the synthesis gas. In this hot gaseous phase, exclusively thermal energy is bonded.

The thermal energy bonded in the gaseous phase is used preferably in a waste heat boiler for the production of steam. The produced steam, the pressure of which should preferably be above 50 bar can be used for production of current in a steam turbine or as heat carrier, for example as long-distance heat.

The gaseous, cooled phase which is discharged from the waste heat boiler is subjected to a cleaning process according to the state of the art in order to bond and extract pollutants present in the gaseous phase, such as sulphur-, chlorine- and nitrogen compounds, heavy metals, dusts, organic compounds etc.

In an advantageous embodiment, the thermal energy dissipated by the interior cooling of the high temperature reactor is used in the waste heat boiler.

In a further advantageous embodiment, the possibility can however also be provided that a partial flow of the uncooled, uncleaned synthesis gas which is removed from the high temperature reactor is subjected to a shock-cooling and subsequently is cleaned. The process takes place hereby as known in the state of the art. The synthesis gas mixture heated above 1000° C. is thereby cooled immediately after leaving the high temperature reactor in a shock-like manner to below 100° C. by means of cold water injection. The liquid and solid particles entrained in the gas flow are absorbed by the cooling water.

The cooled precleaned synthesis gas is subsequently subjected also to a multistage cleaning. The thus obtained synthesis clean gas, comprising hydrogen, carbon monoxide and carbon dioxide, can subsequently be used as energy or material. This embodiment is advantageous in particular when synthesis gas of high quality is intended to be used further for chemical syntheses so that for example the production of fuels is also available. Furthermore, it is however possible that the thus obtained cleaned synthesis gas is recycled for the thermal treatment of waste.

According to the invention, in addition a device for the thermal treatment of waste of all types is also provided, comprising at least one low temperature stage and at least one high temperature stage, the low temperature stage being configured in the form of a horizontal channel which discharges without interruption into a high temperature reactor and also at least one combustion chamber connected to the gas outlet of the high temperature reactor and at least one subsequent at least one-stage waste heat boiler.

It is hereby advantageous if the waste heat boiler is connected to at least one steam turbine and to a subsequent generator.

In a further advantageous embodiment, it is provided that a gas branch is provided between the gas outlet of the high temperature reactor and the combustion chamber, said gas branch being connected to a subsequent shock-cooling (quenching) and to a gas cleaning system.

The invention has the following advantages relative to conventional waste thermoelectric power plants:

-   -   The temperature of the gaseous phase at the gas outlet of the         high temperature reactor at approx. 1000° C. is significantly         above the flue gas temperature of a waste incineration plant         which is generally below 800° C. so that the specific thermal         energy of the gaseous phase is substantially greater.     -   The combustion of the homogeneous synthesis gas is effected         slightly overstoichiometrically, whilst the conventional waste         incineration plant must be operated with a substantially higher         air excess in order that the extremely heterogeneous waste can         be incinerated as completely as possible. The specific flue gas         quantity (Nm³/t) of a waste incineration plant is therefore         substantially above the specific waste gas quantity of the         present invention. The necessary components of the gas cleaning         should correspondingly be designed to be smaller.     -   Furthermore, the specific pollutant loading during incineration         of the heterogeneous waste is substantially greater than the         specific pollutant loading during combustion of the homogeneous         synthesis gas.

The present invention has the following advantages relative to the above-described state of the art in waste gasification:

-   -   The shock-cooling of the gaseous phase by spraying with cold         water and all the devices required for this purpose are         dispensed with.     -   The process water treatment and all the devices required for         this purpose are dispensed with.     -   The evaporation of the cleaned process water is dispensed with.     -   The synthesis gas cleaning, comprising the basic and acidic         washer, the COS catalytic converter, the sulphur wash etc., is         likewise dispensed with.

The cleaning stage used already in the state of the art is used for the waste gas cleaning.

The method proposed here leads to a significant reduction in specific investment and operational costs.

If the entire thermal and chemical energy bonded in the gaseous phase is used in order to convert for example the obtained steam flow into electricity in a steam turbine, the current yield is significantly above the quantity of current which can be achieved by using the synthesis gas in a gas engine or in a gas turbine. Since the proposed method leads to a perceptible reduction in the current consumption of the system, the result is a substantial increase in the current excess which can be delivered to the national grid.

If for example, in a gasification plant corresponding to the state of the art, 10 t/h of waste with a calorific value of 12 MJ/kg are used and also, for starting up and maintaining the gasification process, 60 Nm³/t of natural gas, the entire energy input is 39.3 MW. If the proposed method is used, useable energy of 36.8 MW (=93.6% of the total energy input) is obtained. In the case of an efficiency of the waste heat boiler of 85% and efficiency of the steam turbine of 29%, 9.1 MW current (=23.2% of the total energy input) can be produced. After withdrawal of the current consumption of the system, a current excess of 6.1 MW remains (=15.5% of the total energy input).

If the known methods corresponding to the state of the art are used for current generation of the synthesis gas, the following current excesses can be achieved:

-   -   steam boiler/steam turbine: 1.1 MW (=2.8%),     -   gas turbine: 2.2 MW (=5.6%),     -   gas engine: 3.1 MW (=7.9%).

The higher current yield and the lower specific investment and operational costs substantiate the economic superiority of the proposed method.

The invention is explained subsequently in more detail with reference to FIG. 1.

FIG. 1 shows an embodiment of the method according to the invention in which the high temperature treatment is implemented in a high temperature reactor 1 which is configured as a vertical cylindrical reactor. The high temperature reactor 1 is thereby connected without interruption directly to a feed channel 2. The supplied waste is compacted by the compactor press 3 and pushed through the feed channel 2. Whilst the gas pressure is building up, the thereby forming compacted bales 4 are retained in frictional contact with the hot channel wall only until the entrained liquids and readily volatile materials are evaporated and any restoring forces present of individual components are eliminated and until the entrained organic components have adopted at least partially a binding agent function. In the end effect, dust-free, form-stable and structure-stable crumbly conglomerates are thereby produced. The temperature in the feed channel 2 which is operated under oxygen exclusion does not thereby exceed the temperature of 600° C.

The above-described compacted bales 4 are then, in the region of the inlet opening in the high temperature reactor 1, subjected to an extremely high radiation heat. The sudden expansion associated therewith of residual gases and carbonised material leads to the separation thereof into lumps. The thus obtained solid lumpy material then forms, in the high temperature reactor 1, a gas-permeable bed 5 in which the carbon of the carbonised material is combusted with the help of lances 6 which are operated with combustion gas, such as oxygen, oxygen-enriched air or also further combustion gases, firstly to form CO₂ or CO. The carbonising gases flowing turbulently through the reactor 10 above the bed 5 are cracked in their entirety. A temperature-related reaction equilibrium arises during the synthesis gas formation between carbon, CO₂, CO and the steam expelled from the waste. This crude synthesis gas is then discharged via the crude synthesis gas pipe 7.

Below the gasification bed 5, the mineral and metallic components of the carbonised material which is heated to 2000° C. are melted in the high temperature reactor in the region of the bed 5. The melts enter directly into a subsequent treatment reactor 8 in that they are subjected with the help of further lances 6 which are operated with oxygen to homogenisation at more than 1400° C.

Finally this thus homogenised melt is introduced into a water bath 9. The above-described method course and the device thereby correspond essentially to the so-called “Thermoselect Process” known from the state of the art. Reference is made in this respect e.g. to EP 1 203 060 B1 or to DE 41 30 416 C1 mentioned already at the beginning.

It is now essential to the invention that the uncleaned and uncooled synthesis gas which is discharged from the high temperature reactor 1 via the synthesis gas pipe 7 is guided at a temperature above 1000° C. into at least one combustion chamber 10. Oxidation is now undertaken in this combustion chamber. The process thereby takes place such that a slightly overstoichiometric combustion is effected. As a result, a hot gaseous phase is thereby obtained which comprises hot steam and the hot waste gases from the combustion of the synthesis gas. In this hot gaseous phase, exclusively thermal energy alone is also bonded. Via a further gas pipe 11, this hot gaseous phase as described above is now guided into a waste heat boiler 12. Steam which is guided to a steam turbine 13 is produced in the waste heat boiler. The hot side is thereby designated with 14 and the cold side with 15. The steam turbine 13 can thereby be connected to a generator (G) for generation of current.

The cooled gas leaving the waste heat boiler 12 can then be guided to a gas cleaning system in order to bond and extract any pollutants present, such as sulphur, chlorine and nitrogen compounds, heavy metals, dusts and organic compounds.

The embodiment described in FIG. 1 can also be modified such that, out of the high temperature reactor 1 and in fact here out of the region below the gasification bed 5, the interior cooling present in the high temperature reactor which can be introduced in the wall of the high temperature reactor 1 is likewise also guided into the waste heat boiler 12. As a result, an improvement again in the energy yield can be achieved. 

1. Method for the thermal treatment of waste, wherein the waste is subjected to a high temperature treatment with oxygen and/or air enriched with oxygen at a temperature of above 1000° C., the organic waste components being gasified, the inorganic waste components being melted, the uncooled, uncleaned synthesis gas being oxidised and the thereby obtained waste gas being used thermally.
 2. Method according to claim 1, wherein the high temperature treatment is implemented in a high temperature reactor.
 3. Method according to claim 2, wherein in the uncooled, uncleaned synthesis gas is discharged from the high temperature reactor and is oxidised at least in one separate combustion chamber.
 4. Method according to claim 1, wherein the thermal energy is used in a waste heat boiler for the production of steam.
 5. Method according to claim 4, wherein the obtained steam is used to obtain current.
 6. Method according to claim 4, wherein the steam is used as heat carrier.
 7. Method according to claim 4, wherein the waste gases cooled in the waste heat boiler are subjected to a cleaning.
 8. Method according to claim 2, wherein the thermal energy discharged from the high temperature reactor is used in addition in the waste heat boiler as energy.
 9. Method according to claim 2, wherein a partial flow of the uncooled, uncleaned synthesis gas removed from the high temperature reactor is subjected to a shock-cooling and subsequently is cleaned.
 10. Method according to claim 9, wherein the thus obtained, cleaned synthesis gas is recycled for the thermal treatment of the waste.
 11. Device for the thermal treatment of waste, comprising at least one low temperature stage and at least one high temperature stage, the low temperature stage being configured in the form of a horizontal channel which discharges without interruption into a high temperature reactor and also at least one combustion chamber connected to the gas outlet of the high temperature reactor and at least one subsequent at least one-stage waste heat boiler.
 12. Device according to claim 11, wherein the waste heat boiler is connected to at least one steam turbine and to a subsequent generator.
 13. Device according to claim 11, wherein a gas branch is provided between the gas outlet of the high temperature reactor and the combustion chamber, said gas branch being connected to a subsequent shock-cooling and a gas cleaning system. 